Exhaust gas recirculation (EGR) is a well known technique for reducing levels of harmful Nitrogen Oxides (NOx) in emissions from combustion engines and internal combustion engines in particular. Controlling EGR to the right levels is important to achieve desirable emission levels of NOx, but excessive EGR may negatively impact engine and/or emissions performance.
EGR control strategies tend to estimate EGR quantities and qualities and involve expensive EGR gas measurement arrangements such as that disclosed in U.S. Pat. No. 6,725,848. Such flow measurement arrangements tend to comprise a venturi for measuring the mass flow rates, but constituents, i.e. EGR quality, are calculated based on fuel system models. These models may not be accurate for all conditions and combining several estimation models and inputs can quickly lead to errors in calculating.